Essentially, you had $10,000 when you started, and you have $10,000 now, but because of the delay, you would have had $10,500 if the transaction had closed faster.
That's not a loss you can ever take, even in a regular investment account. You can't deduct from your income, something that was never included in your taxable income in the first place.
On top of that, qualified retirement plans work completely differently. You paid no tax on the money when it was contributed, so everything you withdraw is taxable when you retire. It doesn't matter how much money you have in the account, or whether you have more or less than you contributed, you pay tax on anything you withdraw because you never paid tax on the contribution. Your "deduction" is the fact that if you withdraw less (for whatever reason), you pay less tax.
